docs: def global_set(self, key, value):
          """Set ``key`` to ``value`` globally (not at any particular branch or
          revision)
  
          """
          (key, value) = map(self.pack, (key, value))
          try:
              return self.sql('global_insert', key, value)
          except IntegrityError:
              return self.sql('global_update', value, key)